John Hadley

Hadley, John, 1682–1744, English instrument maker. An optician by trade, Hadley built reflecting telescopes, based on Newton's model, that had greater resolution than the cumbersome refractors then in use. In 1731 he built a reflecting octant, based on Newton's sketch, that prefigured the modern nautical sextant. Hadley was a leading member of the Royal Society.